/Engine/Plugins/Online/OnlineFramework/Source/Party/Public/SocialManager.h
Validates that the target user has valid join info for us to use and that we can join any party of the given type
virtual [FJoinPartyResult](API\Plugins\Party\Party\FJoinPartyResult) ValidateJoinTarget ( const [USocialUser](API\Plugins\Party\User\USocialUser) & UserToJoin, const [FOnlinePartyTypeId](API\Plugins\OnlineSubsystem\FOnlinePartyTypeId) & PartyTypeId ) const